How to initialize the reference member variable of a class?

Question

Consider the following code C++:

    #include

using namespace std;

class Test {
    int &t;
public:
    Test (int &x) { t = x;          


        

Answer 1

My compiler emits this error:

error C2758: 'Test::t' : must be initialized in constructor base/member initializer list

And that's exactly what you must do. References must be initialized in the initializer list:

#include

using namespace std;

class Test {
    int &t;
public:
    Test (int &x) : t(x) {  } // <-- initializer list used, empty body now
    int getT() { return t; }
};

int main()
{
    int x = 20;
    Test t1(x);
    cout << t1.getT() << " ";
    x = 30;
    cout << t1.getT() << endl;
    return 0;
}

Explanation:

If the reference is not in the initiliazer list, it's next to impossible for the compiler to detect if the reference is initialized. References must be initialized. Imagine this scenario:

Test (int &x, bool b) 
{
   if( b ) t = x;
}

Now it would be up to the caller of the constructor to decide if valid code was generated. That cannot be. The compiler must make sure the reference is initialized at compile time.